The present invention refers to a process, an installation and a chamber for reducing the biological activity in storage spaces, such as silos, storage sheds, grain stores, cargo holds in grain transport ships or the like, and particularly for the storage and preservation of grains or other perishable foodstuffs.
The storage of large quantities of agricultural products and principally cereals is problematic with regard to the preservation of the product throughout the period of storage. Losses due to the deterioration of stored grains has been a considerable problem on a worldwide scale and it should be observed that losses of this nature are presently of the order of 30% of the total product stocked in Brazil, about 12% in the USA and as high as 50% in some countries of the African continent.
Cereals are characterized by a high potential energy content. Their availability in thousands of tons makes storage locations an excellent nutrition medium for fungi, bacteria, acarids and insects, provided that the ambient conditions such as temperature and humidity (absolute humidity of the grain and relative humidity of the atmosphere) are favorable. The processes used up to the present involve a storage system which controls such parameters so as to reduce biological activity to a minimum. The controls act on the following variables:
Reduction of the absolute humidity of the grain by previous drying.
Constant airing of the storage ambient so as to reduce the fungi population by entertainment of the spores and to reduce the temperature increased as a result of biological activity.
Utilization of gases such as nitrogen (N2), carbon dioxide (CO2) and other gases with the basic purpose of reducing the concentration of oxygen and thus producing a reduction in the aerobic organisms population as well as the metabolism of the grain itself.
Use of toxic chemical products to reduce the amount of microorganisms and insects by intoxication.
All these processes have limited efficiency and some present health risks to the consumers, particularly those related to the use of toxic chemical products.
According to the most recent scientific works regarding the inter-relation of the various variables within a mass of cereals, fungi have been identified as one of the most important elements in the matrix of the echo-system. The following works can be cited as being of special importance: 1) Sinha R.N., Van Bronswijk J.E.M.H., Wallace H.A.H., C.M.A. Journal, Aug. 1, 1970, Vol. 103, 300-301 2) Sinha R.N., Van Bronswijk J.E.M.H., Environm. Entomology 2: 142, 1973 3) Sinha R.N., Journal of Economic Entomology, Vol 64, 1, 3-6. 4) Mori M., Onoue Y., Takahashi T., Chounan S., Moriya K., J Antibact. Antifung. Agents Vol. 15 N.degree. 12, P 601 -605, 1987. 5) Griffiths A.D., Hodson A.C., Christensen C.M., Journal of Economic Entomology, Vol. 52, N.degree. 3, pag. 516-518. 6) Sinha R.N., Harasymek L., Enviromental Entomology Vol 3, N.degree. 2, pags. 244, 246. 7) Tadros, M.S., Vestnik Ceskoloveniske Spolecnosti Zoologicke, Svazek XXXIX, Cislo 4, 1975, Str. 293-296.
The above works show that the elimination of fungi in the stored mass results in the reduction over a period of time of the population of insects and acarids. It is important to note that not only fungivorous organisms depend on fungi but also all larva which, after hatching of the eggs, need fungi to be able to create their digestive systems.
A device for oxidizing particles in suspension in air is already known from Brazilian patent PI 8302255 (U.S. Pat. No. 4,877,990) and European patent 281.551 of the present inventor. Such device creates the generation of high power density within ducts provided in a refractory ceramic block by means of a resistance wire passing through such ducts. These devices are suitable for small and medium sized ambients but are not specially adequate for large areas, such as large stores for the stocking of grain.
Brazilian patent application PI 8502832 of the present inventor discloses a system for the preservation of agricultural products by sterilizing the air. That system uses U-shaped pipes or tubes inside silos, each tube being formed with various orifices in both of its vertical arms and one of the arms having in its interior an apparatus of the type disclosed in Brazilian patent PI 8302255 (U.S. Pat. No. 4,877,990). Such a system, however, was found to have the following disadvantages:
reduced preservation capacity per apparatus: the maximum amount with which satisfactory results of air sterilization were obtained is limited to about 200 kg of stocked product per apparatus;
grain damage: heat generation within the silo tends to dehydrate the stocked grain, thus prejudicing its preservation; and
necessity to adapt the interior of the silos: the same number of U-shaped pipes as of the necessary apparatuses has to be installed within the silos.
Another disadvantage of the prior art grain storage systems is related to the generation of static electricity in view of friction between individual grains, in particular at the time of storage, and this may generate discharges that can cause explosions should there be any inflammable gases in the silo or shed, or even serious injury or death to persons within the silo.
Considering the prior art, the object of the present invention is to eliminate fungi from storage ambients so as to permit agricultural products to be preserved without the use of chemicals, as well as to permit the storage of the product with high absolute humidity content, in a totally new manner and without damaging the sorted grain.
A further object of the invention consists in eliminating the electrostatic charge in the stored product so as to avoid the resulting disadvantages and risks.
The process by which the above objects may be reached is characterized by the following steps:
gradually extracting the air from the ambient; ambient;
oxidating air within a chamber located outside the ambient;
forcing the processed air into the ambient.
The above process may be applied in closed, open or mixed circuit, that is to say, the air may circulate permanently without exchange with the atmosphere, or fresh processed air may be admitted to the ambient together with total removal of the air previously within the ambient, or further, part of the air may be circulated and the rest admitted from outside.
The use of as closed circuit, however, has the advantage that the air of the storage ambient is gradually sterilized with respect to the presence of microorganisms until almost total sterilization is obtained. Apart from this, a closed circuit permits one to obtain a hydrostatic balance between the air and the stored product.
The new concept presently proposed consists in introducing to the storage ambient regular volumes of sterilized air, sterilization being obtained by subjecting the air to elevated temperatures, of the order of 500.degree. C,. and subsequently cooling the air before it is pumped into the storage ambient. The air is heated in such a manner that heat is not dissipated within the storage ambient, so as to permit temperature and humidity conditions to be maintained within the desired parameters.